EPD (or called E-paper, E-ink) adopts a display technique different from the conventional displays such as a cathode ray tube (CRT) and liquid crystal display (LCD). An EPD has multiple micro cups in a substrate that contain a colored dielectric solvent and a plurality of charged colored particles suspended in the colored dielectric solvent. There are two electrodes on outer sides of the micro cups. Through the two electrodes, the potential difference at the edges of the micro cups can be changed and the charged colored particles are attracted by magnetic forces and moved to an electrode of an opposite polarity. The movement of the charged colored particles changes the color displayed on the surface of the substrate. References of control principle and methods can be founded in R.O.C. patent publication No. 538263 entitled “Electrophoretic display” and R.O.C. patent publication No. 200832031 entitled “Electronic paper apparatus and manufacturing method thereof”. Basically they adopt the electrophoretic principle and fundamental structure previously discussed by controlling the potential difference to change the color displayed on the surface. The characteristic differences of the EPD technique and CRT and LCD are known in the art, thus are omitted here. A key technique to control EPD effect is controlling the potential difference applied on the substrate electrodes, the greater the potential difference applied the electrodes, the faster the movement of the charged colored particles. Otherwise, the movement speed of the charged colored particles is slower. The movement distance of the charged colored particles in the micro cups can be divided into multiple sections to form a grey level. The time required for driving all the charged colored particles in the micro cups in the substrate to move once is called a frame time. To control the picture change of the EPD, a control circuit is provided to judge the alteration extent of a next picture through an image processing unit, and a driving unit is provided to apply a potential difference on the electrodes. Hence the control circuit, according to the position of the charged colored particles in the micro cups of the previous picture, can determine the moving distance required by the charged colored particles. Then, through a look up table, the pixel position where the potential difference has to be applied can be obtained. Thereby the potential difference is applied on the electrodes to renew the picture.
The accuracy and speed of the movement position of the charged colored particles affect picture quality and renew speed. Given a same potential difference applying on the electrodes, the movement speed of the charged colored particles is affected by the colored dielectric solvent. When temperature alteration extent is greater, the resistance received by the charged colored particles moving in the colored dielectric solvent changes significantly. In general, a higher temperature results in a greater fluidity of the colored dielectric solvent and the charged colored particles move at a faster speed. On the contrary, a lower temperature results in a lower fluidity of the colored dielectric solvent and a slower moving speed of the charged colored particles. But the conventional control circuit usually does not change the driving voltage or applied voltage difference time with temperature alterations during operation, as a result in extreme operation conditions the problem of color variation or display error occurs. While the conventional techniques also try to use multiple look up tables to match different use temperatures, such as searching a look up table A during 10° C.˜30° C., and searching another look up table B during −5° C.˜9.9° C. and the like. But using more look up tables requires at least two times of memory capacity for the EPD driving circuit to store the look up tables. As a result, more memory is occupied on the crowded circuit board. The additional memory also increases the cost.
Hence there is still room for improvement in terms of providing an adjustment circuit at a lower cost to maintain the picture quality of the EPD at different operation temperatures.